I've thought about this quite a bit myself and wonder who does the choosing.

Perhaps its all at random? I view time as cyclic, and so all of this will repeat itself again - probably in a slightly different pattern though. That being said, perhaps everything is set on random when it comes to the awareness held by an "individual" aspect of the grand scale fractal machine. At some point your individual awareness shall experience everything there is to experience. You will be the rock outside your house at some point. In another instance you'll be the keyboard I am typing on. Yet another you'll be a molecule making up a foreign planet to our own.